#include<stdio.h>
//int prime (int n) nothing being returned (before)
void prime (int n) //after, changed return type to void.
{
    //int n, c = 2; removed the second 'n' declaration (before) since it is defined in the function signature.
    int c = 2; // (after)
    if ( n % c == 0 )
    {
        printf("%d is not prime.\n", n);
    }
    else
    {
        printf("%d is prime.\n", n);
    }

}
int main()
{
    int n;
    printf("Please enter a number:\n");
    scanf("%d", &n);
    prime (n);

    return 0;
}